During operation of fluorescent lamps, as a result of various effects, regions on the filaments can form which impair or even entirely prevent the emission capability of the emitter. In particular the deposition of impurities or of eroded material and the resultant conversion processes need to be included in these effects. The mentioned regions are therefore available for the emission to a restricted extent or no longer available at all, as a result of which the maximum possible life of the lamp is not reached.
Permanent filament heating in order to prevent such depositions is undesirable as a result of the permanent losses associated therewith, which result in considerable impairment of the efficiency of the fluorescent lamp, and as a result of the heating of the cold spot for the Hg vapor pressure setting. The heating of the filaments for starting the fluorescent lamp is very short, i.e. this heating operation is less than 0.5 s and is predominantly inhomogeneous. As a result, it is not possible either for deposits to be removed or prevented.